Spread 1 tablespoon mayonnaise on one side of bread, repeat on second slice with remaining tablespoon of mayonnaise. Melt ½ tablespoon of butter in a non-stick skillet. Once melted place 1 slice of bread, mayonnaise side down; spread 1 tablespoon of pizza on top; layer with mozzarella cheese and pepperoni slices and remaining slice of mozzarella cheese; salt and pepper to taste. Spread remaining tablespoon of pizza sauce on second slice of bread, place on top of sandwich, mayonnaise side up. Cook until underside is golden brown, about 4 minutes, turn sandwich and add remaining ½ tablespoon of butter to skillet. Slightly press down on sandwich to evenly brown bread and melt cheese, about 3-4 minutes.